When recording information on a magnetic disk, for example, a flexible magnetic disk such as a floppy disk, the floppy disk is rotated and information is recorded on the annular tracks. In general, a guard band is provided between two adjacent tracks. The guard band is provided in order to absorb a tracking error caused by expansion or contraction of the floppy disk due to changes in temperature and by a positioning error due to precision of a head tracking mechanism.
Many types of magnetic recording devices using a floppy disk as a magnetic recording medium are available. For example, still picture recording device such as a so-called electronic still camera is known in the art. An image of a subject obtained through a lens is converted to an electrical signal and recorded onto a floppy disk. The floppy disk used for this purpose is called a video floppy disk. For reproduction, a device is used in which the floppy disk is rotated and the video signal recorded on the track is reproduced as a still picture on a display device such as a television receiver. In these devices, one field of video signals is recorded on one turn of the track. The method in which a still picture is reproduced from a one-field video signal is referred to as field recording/reproduction. Another method in which each field of the video signal from the same frame is on each of two tracks and the video signals from the two tracks are reconstructed to reproduce a single still picture is referred to as frame recording/reproduction. According to the specifications for electronic still cameras, the floppy disk is rotated at a speed of 3,600 rpm, and tracks of 60 .mu.m in width are concentrically formed with a pitch of 100 .mu.m. The guard band has a nominal width of 40 .mu.m, and allowance of the track radius for expansion and contraction of the floppy disk is specified as .+-.14 .mu.m.
When displaying a still picture on a television receiver or the like, the simultaneous output of sound or music has been taught as in Japanese Patent Applications Laid-open Nos. 129701/1986 and 153803/1986 which respectively disclose methods for recording such information on the guard band. In these methods, the normal track is used as a main track for recording a video signal, and an information signal such as sound or the like, which is compressed with respect to time, is recorded on the guard band between the main tracks, so that the relative azimuth between the main track and the guard band is adjusted. At reproduction, the recorded time-compressed information is expanded to the original time base. A magnetic head for recording the video signal on the main track and a magnetic head for recording the information signal on the guard band may be provided independently of each other, or integrally provided as proposed in the Japanese Patent Application Laid-open No. 129701/1986.
After the corresponding video signal is recorded on the main track, the information signal is recorded on the guard band adjacent to the main track.
As for the recording current, when the main track magnetic head and the guard band magnetic head have the same characteristics, both heads are applied with recording currents of the same value. This is because the video signal and the time-compressed information signal have almost the same frequency range and, in turn, have the same optimum recording current value. When the magnetic heads have different characteristics such as in number of coil turns, the magnetic heads normally have different optimum recording current values, but have almost the same magnetomotive forces. This is also true when the main track and the guard band are respectively recorded with video signals, or when the main track and the guard band are respectively recorded with any signals having almost the same frequency range.
As described above, a tracking error inevitably occurs. Therefore, as shown in FIG. 5, information is recorded on the guard band overlapping part 3 of a main track 2 of a magnetic disk 1. In this case, when information is already recorded on the main track 2, the information on the overlapped part 3 will be deteriorated. In FIG. 5, numeral 4 indicates the guard band, and numeral 5 indicates an information recording area which is recorded by the guard band magnetic head.
On the other hand, an integral type magnetic head disclosed in Japanese Patent Application Laid-open No. 129701/1986 has a sound signal recording magnetic head which is put between two video signal recording magnetic heads, and both side surfaces of the sound signal recording magnetic head closely contact over large areas with side surfaces of the video signal recording magnetic heads. The magnetic head having such a structure has a strong magnetic coupling between adjacent magnetic heads, and each signal flux leaks into adjacent magnetic heads which results in noises, that is so-called cross talk. As a result, the reproduced picture may be considerably disturbed, or noises may occur. Therefore, the above-described integral type magnetic head is defective and not suitable for practical use. No magnetic head has previously been developed which can satisfactorily record or reproduce information on both the main track and an adjacent guard band of the floppy disk.